Prior art workers have devised numerous types of conveyors and stackers utilizing rotating screws having helical threads. For example, U.S. Pat. No. 3,063,577 in the name of Albert F. Shields, issued Nov. 13, 1962, teaches a stacking, straightening and delivery device for box blanks utilizing a pair of helically threaded screws. The box blanks are introduced between the screws which lift the box blanks upwardly. As the blanks move upwardly, they are evenly spaced by the thread pitch of the screws. When a predetermined number of blanks moves above the top of the screw threads, a pusher means removes them from the device. A similar device is taught in U.S. Pat. No. 3,203,561 in the name of Albert F. Shields, issued Aug. 31, 1965.
U.S. Pat. No. 3,712,487, issued in the name of Jurg Eberle on Jan. 23, 1973 teaches a stacking device for substantially flat objects such as paper products, utilizing one or more worm-like conveyor elements rotated about their longitudinal axes and extending between an infeed station and a delivery station. The products are continuously accumulated in a stack at the upper end or ends of the one or more worm-like conveyor elements. U.S. Pat. No. 4,108,319 teaches an accumulator for sheets of glass comprising two pairs of helically threaded rotating shafts. The glass sheets are introduced between the pairs of shafts and are lifted by the helical shaft threads vertically to form a stack at the upper termination of the threads.
U.S Pat. No. 3,280,679 issued to Harold W. Huffman on Oct. 25, 1966 describes a device for receiving individual sheets, lowering each sheet onto the top of a preceding sheet to make a stack thereof containing a predetermined number of sheets. When the predetermined number of sheets is achieved, the entire stack of sheets is vertically discharged, as a unit, onto a conveyor. To this end, a pair of piling screws are provided in side-by-side relationship, with a pair of batching screws located therebeneath. Each batching screw is coaxial with one of the piling screws. The piling screws cooperate to act as a conveyor to lower individual sheets onto the thread plates of the batching screws until a stack of sheets of predetermined number has accumulated thereon. Thereafter, the batching screws make one revolution to deposit the stack on a conveyor. Between depositing revolutions, the batching screws are stationary.
Prior art stacking devices, utilizing helically threaded screws, simply use the screws as vertical conveying means, shifting products vertically upwardly or downwardly, one-by-one. The products are accumulated at the upward or downward terminations of the screw threads. Additional, intermittent means such as pusher means, batching screws or the like are needed to form stacks of a specific count. As a result, mechanical parts utilizing intermittent motion are required and such stacking devices are speed limited.
The present invention is based upon the discovery that one or more cooperating pairs of screws, having properly configured helical threads, can, themselves, be utilized to form product stacks of specific count, the products of each stack being aligned. The stacker of the present invention will accept single or multiple product input and is capable of high speed operation using continuous motion. One or more pairs of continuously rotating single-thread screws can be utilized in conjunction with the one or more pairs of stacker screws to simply convey the stack formed by the stacker screws, or to accumulate and convey the stacker screw stacks, depending upon the rotational speed of the single-thread screws, relative to the stacker screws.